Bleaching of polyamides



BLEACHING F POLYAMIDES Alhertus Gerardus Lutgerhorst, Arnhem,Netherlands, assignor to N. V. Onderzoekingsinstituut Research, Arnhem,Netherlands, a corporation of the Netherlands No Drawing. ApplicationApril 9, 1953, Serial No. 347,839

Claims priority, application Netherlands August 7, 1952 7 Claims. (Cl.8-109) This invention relates to the bleaching of textile materials madeof synthetic linear polyamides of the nylon type. Examples of suchsynthetic linear polyamides are those described in U. S. patents such asNos. 2,071,250, 2,071,253, 2,130,948 and 2,359,877. These syntheticlinear polyamides are characterized by the presence of repeatingcarbonamide units having the structural formula One of the principalobjects of the present invention is to provide a new and improved methodfor bleaching textile materials of the kind indicated, either in theform of artificial threads or fibers or in the form of fabrics knit orwoven from such threads or fibers, in such manner as to bleach themwithout impairing the strength of the fibers in any way. A furtherobject of the invention is to provide a method for successfullybleaching polyamide materials of the foregoing nature with hypochloritesolutions while avoiding previously known disadvantages attendant uponthe use of hypochlorite solutions for the purpose indicated.

The manner in which these and other objects and features of theinvention are attained will appear more fully from the followingdescription thereof, in which reference is made to typical and preferredprocedures in order to indicate more fully the nature of the inventionbut without intending to limit the invention thereby.

It has long been known in the art that the bleaching of textilematerials consisting essentially of synthetic linear polyamides givesrise to serious difiiculties. This is true both for fibers and threadsconsisting of these polyamides as well as for fabrics knit or woven fromsuch fibers or threads, and especially in the case of finished articlesmade from such knit or woven fabrics. One of the more seriousdifliculties known to be encountered in the case of treatment of thesematerials is that upon high temperature stabilization, known per se, aslight discoloration often results.

It is also known that if one attempts to bleach these synthetic linearpolyamide materials with hypochlorite solutions, such as NaOCl orCa(OCl)z solutions, a considerable amount of chlorine is adsorbed orchemically bound by the fiber or thread undergoing treatment, whichchlorine is not removed by any normal treatment with known anti-chloragents. Owing to this retained residual chlorine, there occurs a seriousdecline in the strength of the fibers making up the textile material sothat as a consequence the bleaching of nylon fabrics with hypochloritesolutions cannot be employed, and the literature warns against it. Eventreatment with anti-chlor reagents at somewhat increased temperatures,e. g., 40-60 C., has been found to give no improvement in this respect,and consequently such fabrics have heretofore been of necessity bleachedwith chlorite solutions, such as NaClOz, in acid medium. Although goodresults may be obtained in this way, nevertheless the step of bleachingwith chlorite entails considerable technical objections because thechlo- 2,727,804 Patented Dec. 20, 1955 "ice rite-especially in thesomewhat acid solutions and at the relatively high temperatures employedrequired for its use in bleachingis extremely reactive with respect toalmost all materials of construction that would normally be employed forconstructing the apparatus in which the bleaching treatment is carriedout. Moreover, the C102 that may be evolved from the chlorite solutionis extremely toxic.

In accordance with the present invention, however, it has beendiscovered that all textile materials consisting essentially ofsynthetic linear polyamides may be bleached with excellent resultswithout impairing the strength of the fiber provided said textilematerials are first treated with a hypochlorite solution and then with areducing agent at a temperature above C.

Particularly desirable results are obtained when one employs as thereducing agent a solution of a hydrosulfite (Na-28204) or one of itsderivatives at a temperature of -95 C.

The antecedent bleaching operation may be performed in different waysand also at widely differing pH values. For example, the bleaching maybe performed at room temperature with a hypochlorite solution containing0.5 g./l. of active chlorine at a pH of either 8-10 or 3-4, and over aperiod that may vary from 15 minutes to 2 hours. Thereupon, anaftertreatment with a hydrosulfite solution (for example, 1 g./l. ofNa2S2O4) at 90-95 C. completely removes all the retained chlorine fromthe fiber. For this purpose a time of treatment of five minutes isgenerally sufiicient, but this may be extended for example to 30minutes, if desired.

Although nearly all the ordinary reducing agents such as aqueoussolutions of bisulfite, thiosulfate, sulfite, and similar reagents havebeen found to be capable of removing the retained chlorine from thenylon articles during the subsequent anti-chlor treatment attemperatures higher than 80 C., the bleaching effect obtained wassometimes less satisfactory than after a treatment with aqueoussolutions of hydrosulfite and its derivatives, such as the form aldehydeaddition compound or the zinc-formaldehyde addition compound ofhydrosulfite. These latter compounds have the additional advantage ofbeing more stable at the relatively high temperatures employed for theaftertreatment, and are therefore preferred.

The outstanding effect obtained in accordance with the method of thepresent invention is all the more surprising, since the application tothe nylon fabric of a reducing agent alone, even at high temperature,results in only a very slight bleaching effect.

The presence or absence of retained chlorine can easily be shown bymeans of an acidified potassium iodide solution which, even in thepresence of mere traces of chlorine in the material, gives an intensiveyellow coloration. As soon as all the residual chlorine has beenremoved, however, no coloration occurs upon testing with the acidifiedpotassium iodide solution.

After rinsing and drying the nylon articles bleached according to themethod of the present invention, the whiteness thereof is as good as, orfrequently even better than, that which can be obtained by bleachingwith a chlorite solution. It will be apparent therefore that whenproceeding in accordance with the present invention all the objectionsinherent in carrying out the bleaching operation with chlorite (C102)are eliminated, and at the same time the conventional apparatus known inthe art for bleaching with hypochlorite may be employed.

The bleaching agent may be employed in the form of calcium hypochloritesolutions or alkali metal hypochlorite solutions such as sodium orpotassium hypochlorite solutions, and the reducing agents may beemployed in the form of their alkali metal salt solutions such as sodiumor potassium salt solutions or, in the case of the hydrosulfite,solutions of the addition compounds referred to above.

I am aware that it has been suggested heretofore to bleach nylon fibersand the like with sodium hypochlorite solution followed by declorinationin an acid sodium bisulfite bath (see Diserens, Neueste Fortschritte undVerfahren in der chemischen Technologie der Textilfasern, Part 2, NeueVerfahren in der Technik der chemischen Veredlung der Textilfasern, vol.I, paragraph bridging pages 577-8) but there is no indication inDiserens that the subsequent antichlor treatment must be conducted atrelatively high temperatures. In fact, Diserens indicates that while inmany cases his process gives good results, nevertheless it isinsuflicient for pure white and he goes on to recommend bleaching withsodium chlorite or with chlorine dioxide.

While specific examples of preferred methods and reagents embodying thepresent invention have been described above, it will be apparent thatmany changes and modifications may be made in the methods of procedureand in the reagents without departing from the spirit of the invention.It will therefore be understood that the examples recited and theparticular proportions and methods of procedure set forth above areintended to be illustrative only, and are not intended to limit theinvention.

What is claimed is:

l. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising treating such materials with ahypochlorite, and then with a reducing agent at a temperature above 80C.

2. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising treating such materials with asolution yielding hypochlorite ions, and then with a solution of areducing agent at a temperature higher than 80 C.

3. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising bleaching such materials with anaqueous solution of a hypochlorite selected from the class consisting ofcalcium and alkali metal hypochlorites, and then with an aqueoussolution of a reducing agent at a temperature of about 90-95 C.

4. A method as defined in claim 3 wherein the reducing agent is ahydrosulfite.

5. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising treating such materials with anaqueous solution yielding hypochlorite ions, rinsing the textilematerials in order to remove most of the hypochlorite solution, andthereafter removing residual chlorine from said textile materials bytreating same with an aqueous solution of a compound selected from theclass consisting of hydrosulfites and addition compounds ofhydrosulfites at a temperature above C.

6. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising treating such materials with anaqueous solution of a hypochlorite selected from the class consisting ofcalcium and alkali metal hypochlorites, rinsing the textile materials inorder to remove most of the hypochlorite solution, and thereafterremoving residual chlorine from said textile materials by treating samewith an aqueous solution of a compound selected from the classconsisting of hydrosulfites and addition compounds of hydrosulfites at atemperature of approximately -95 C.

7. A method for the bleaching of textile materials comprising asynthetic linear polyamide comprising treating such materials with anaqueous solution of a hypochlorite selected from the class consisting ofcalcium and alkali metal hypochlorites, rinsing the textile materials inorder to remove most of the hypochlorite solution, and thereafterremoving residual chlorine from said textile materials by treating samewith an aqueous solution of sodium hydrosulfite at a temperature ofapproximately 90-95 C.

Turnbull: Dyeing of Broad-Woven Nylon Fabrics, Am. Dyest. Reporter,October 17, 1949, p. 747.

Diserens: Neueste Fortschritte und Verfahren in der chemischenTechnologie der Textilfasern, part 2, Neue Verfahren in der Technik derchemischen Veredlung der Textilfasern, vol. 1, pp. 577 to 580,Birkhauser, Basel,

1. A METHOD FOR THE BLEACHING OF TEXTILE MATERIALS COMPRISING ASYNTHETIC LINEAR POLYAMIDE COMPRISING TREATING SUCH MATERIALS WITH AHYPROCHLORITE, AND THEN WITH A REDUCING AGENT AT A TEMPERATURE ABOVE80*C.